An actuator has been known that is used for a safety device for an automobile (cf. Patent Document 1, for example). The actuator described in Patent Document 1 includes a housing, which is a cylindrical cylinder; a piston rod; and a gas generator. The gas generator is positioned at one end side of the housing in an axial direction. Further, prior to driving, the piston rod is accommodated in an inner part of the housing, and, during driving, the piston rod extends out from the other end side of the housing in the axial direction while sliding along an inner wall of the housing.
In the above-described actuator, upon generating high pressure gas in the gas generator, the high pressure gas acts on a surface of the piston rod that faces the gas generator at the one end side in the axial direction, so that the piston rod is pressed toward the other end side in the axial direction. In this case, the piston rod extends out from the other side of the housing in the axial direction while sliding along the inner wall of the housing, so that the actuator extends in the axis direction.